System for controlling starting of air conditioner and control method thereof

ABSTRACT

A system for controlling the starting of an air conditioner includes a compressor controlled in a pulse width modulation according to a duty cycle control signal, an electronic expansion valve for expanding refrigerant compressed in the compressor, a high pressure conduit connecting the exit side of the compressor and the inlet side of the electronic expansion valve, a low pressure conduit connecting the exit side of the electronic expansion valve and the inlet side of the compressor, a bypass conduit connected at its first end to the high pressure conduit and at its second end to the low pressure conduit, and a flow rate regulating valve mounted on the bypass conduit for regulating a flow rate of fluid flowing through the bypass conduit. A control unit controls the compressor during the starting of the compressor in such a way that the electronic expansion valve is open, the flow rate regulating valve is open and a duty control signal shorter than a duty control signal during a normal operation is generated.

TECHNICAL FIELD

The present invention relates generally to air conditioners, and inparticular to a system and method for controlling the starting of an airconditioner that employs a pulse width modulated compressor.

BACKGROUND ART

With the enlargement of buildings, there is an increasing consumerdemand for a multi-air conditioner in which a plurality of indoor unitsare connected to a single outdoor unit. In such a multi-air conditioner,the length of each refrigerant conduit connecting each indoor unit tothe outdoor unit is long because the outdoor unit is relatively far awayfrom the indoor unit, so the amount of filled refrigerant is large andliquid refrigerant can enter the compressor during the starting of theair conditioner.

In particular, if power supply to any indoor unit is abruptly cut offduring the operation of a multi-air conditioner, there is increased apossibility that fluid refrigerant enters the compressor. When the powerof an operated indoor unit is abruptly cut off during operation, anelectronic expansion valve is not closed because power supply to theelectronic expansion valve constituting an element of the indoor unit iscut off. Accordingly, high pressure liquid refrigerant situated in arefrigerant conduit between the condenser and the electronic expansionvalve enters the compressor or an accumulator upstream of the compressorthrough the electronic expansion valve and the evaporator in anon-evaporated state.

This phenomenon is continued until the pressures of high and lowpressure sides are balanced. The liquid refrigerant having entered thecompressor is mixed with oil contained in the compressor to dilute theoil, so the lubrication of the friction portions of the compressor isdeteriorated, thereby damaging the compressor.

Meanwhile, for the multi-air conditioner, a great cooling capacity isrequired and each indoor unit is frequently turn on/off, so the requiredcooling capacity is changed. In order to meet such a demand, a variablerotation number compressor having a large and variable capacity isemployed in the multi-air conditioner. In such a variable rotationnumber compressor, the capacity of the compressor is regulated to besuitable for a variation in required cooling capacity in such a way thatthe rotation number of a motor is controlled by varying the frequency ofcurrent applied to the motor in an inverter control manner. However, theconventional variable rotation number compressor is problematic in thatthe rotation number of its motor cannot be controlled with a desirableresponse and a precision because the motor being rotated has to becontrolled directly according to a required cooling capacity.Additionally, since the rotation number of the motor is frequentlyvaried, vibrations and noises occur, thereby causing problems that thelife spans of the motor and the compressor are shortened and themechanical reliability of an entire system is deteriorated.

In addition, since an expensive and complicated circuit device isrequired and power consumption is great in order to vary the frequencyof current applied to the motor, the conventional variable rotationnumber compressor is less efficient than a general compressor.Particularly, in the conventional variable rotation number compressorare required several power conversions of initially inputted commercialAC power into DC power and this DC power into AC power having a requiredfrequency through converters, so the structure of the circuit device iscomplicated and noises are frequently generated in the circuit device.

In addition, a large-capacity, variable rotation number compressor isproblematic in that it is difficult to control the compressor, theefficiency of the compressor is low, the size of the compressor is largeand the cost of the compressor is high, so it is difficult to fulfilllarge-capacity requirements with the variable rotation numbercompressor. Accordingly, in order to fulfill a large capacityrequirement two or more compressors are employed. In this case, astandard compressor in which its motor is rotated at a constant speed isgenerally utilized together with the variable rotation numbercompressor. If a plurality of compressors are utilized, the entire sizeof an outdoor unit is enlarged and, accordingly, the handling of theoutdoor unit becomes difficult.

Pulse width modulated compressors are disclosed as other variablecapacity compressors in U.S. Pat. No. 6,047,557 and Japanese UnexaminedPat. Publication No. Hei 8-334094. These compressors are utilized inrefrigerating systems each having a plurality of freezing compartmentsor refrigerating compartments, and designed to be directly applied toshort piping in which the portion of a refrigerant conduit situatedbetween a compressor and an evaporator is short. Consequently, thesecompressors cannot be applied to air conditioning systems for buildingsthat indispensably employ long piping and are given control environmentsdifferent from those for the refrigerating systems. Additionally, in theprior art, there is not disclosed a control system and method forutilizing a pulse width modulated compressor in an multi-airconditioner, and in particular a control system and method for rapidlyand safely performing the starting of an air conditioner.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a system and method for controlling the startingof an air conditioner employing a pulse width modulated compressor,which is capable of rapidly and safely performing the starting of theair conditioner.

Another object of the present invention is to provide a system andmethod for controlling the starting of an air conditioner, which iscapable of preventing the inflow of liquid refrigerant in the airconditioner employing a pulse width modulated compressor.

In order to accomplish the above objects, in accordance with theprinciples of the present invention, a system for controlling thestarting of an air conditioner comprises a compressor controlled in apulse width modulation manner according to a duty control signal; anelectronic expansion valve for expanding refrigerant compressed in thecompressor; a high pressure conduit connecting the exit side of thecompressor and the inlet side of the electronic expansion valve; a lowpressure conduit connecting the exit side of the electronic expansionvalve and the inlet side of the compressor; a bypass conduit connectedat its first end to the high pressure conduit and at its second end tothe low pressure conduit; a flow rate regulating valve mounted on thebypass conduit for regulating a flow rate of fluid flowing through thebypass conduit; and a control unit for controlling the compressor duringthe starting of the compressor in such a way that the electronicexpansion valve is opened, the flow rate regulating valve is opened anda duty control signal shorter than a duty control signal for a normaloperation is generated.

Additionally, in accordance with another aspect of the principles of thepresent invention, a system for controlling the starting of an airconditioner, comprising: a compressor controlled in a pulse widthmodulation manner according to a duty control signal; an electronicexpansion valve for expanding refrigerant compressed in the compressor;a high pressure conduit connecting the exit side of the compressor andthe inlet side of the electronic expansion valve; a low pressure conduitconnecting the exit side of the electronic expansion valve and the inletside of the compressor; a bypass conduit connected at its first end tothe high pressure conduit and at its second end to the low pressureconduit; a flow rate regulating valve mounted on the bypass conduit forregulating a flow rate of fluid flowing through the bypass conduit; anda control unit for controlling the flow rate regulating valve, theelectronic expansion valve and the compressor to prevent liquidrefrigerant from entering the compressor during a starting operation ofthe compressor.

Additionally, in accordance with yet another aspect of the principlesthe present invention, a method for controlling the starting of an airconditioner comprises determining whether a starting signal is inputtedto a compressor controlled in a pulse width modulation manner accordingto a duty control signal; and operating the compressor for apredetermined time while closing the electronic expansion valve andopening the flow rate regulating valve mounted on the bypass conduitconnecting exit and inlet sides of the compressor, when the startingsignal is inputted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the cycle of a system for controlling thestarting of an air conditioner in accordance with the present invention;

FIG. 2a is a sectional view showing a pulse width modulated compressorin a loading position, and FIG. 2b is a sectional view showing the pulsewidth modulated compressor in an unloading position;

FIG. 3 is a graph showing a relationship among a loading time, anunloading time and the amount of discharged refrigerant during theoperation of the compressor of FIGS. 2a and 2 b;

FIG. 4 is a block diagram showing the system for controlling thestarting of an air conditioner in accordance with the present invention;and

FIG. 5 is a flowchart showing a method for controlling the starting ofan air conditioner in accordance with the present invention.

DESCRIPTION OF REFERENCE CHARACTERS OF PRINCIPLE PARTS

2: compressor

4: electronic expansion valve

5: evaporator

8: outdoor unit

9: indoor unit

13: vent valve

16: hot gas valve

17: liquid valve

26: pulse width modulated valve

27: outdoor control unit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention are described indetail with reference to accompanying drawings. FIG. 1 is a diagramshowing an embodiment of the cycle of a system for controlling thestarting of an air conditioner in accordance with the principles of thepresent invention. The air conditioner 1 of the present inventionincludes a compressor 2, a condenser 3, a plurality of electronicexpansion valves 4, and a plurality of evaporators 5, which areconnected to each other by refrigerant conduits to form a closedcircuit. Of the refrigerant conduits, a refrigerant conduit connectingthe outflow side of the compressor 2 to the inflow side of theelectronic expansion valves 4 is a high pressure conduit 6 for guidingthe flow of high pressure refrigerant discharged from the compressor 2,while a refrigerant conduit connecting the outflow side of theelectronic expansion valves 4 to the inflow side of the compressor 2 isa low pressure conduit 7 for guiding the flow of low pressurerefrigerant expanded in the electronic expansion valves 4. The condenser3 is situated on the high pressure conduit 6, while the evaporators 5are situated on the low pressure conduit 7. While the compressor 2 isoperated, refrigerant flows in solid arrow directions.

The air conditioner 1 includes an outdoor unit 8 and a plurality ofindoor units 9. The outdoor unit 8 includes the above describedcompressor 2 and condenser 3. The outdoor unit 8 further includes anaccumulator 10 situated on the low pressure conduit 7 upstream of thecompressor 2 and a receiver 11 situated on the high pressure conduit 6downstream of the condenser 3. The accumulator 10 serves to collect andevaporate liquid refrigerant having not been evaporated and allowevaporated refrigerant to flow into the compressor 2. If refrigerant isnot evaporated completely in the evaporators 5, refrigerant entering theaccumulator 10 is a mixture of liquid refrigerant and gaseousrefrigerant. The accumulator 10 evaporates liquid refrigerant, andallows only gaseous refrigerant (gas refrigerant) to enter thecompressor 2. To this end, it is desirable to situate the entrance andexit ends of the refrigerant conduit in the upper portion of theaccumulator 10.

If refrigerant is not condensed completely in the condenser 3,refrigerant entering the receiver 11 is a mixture of liquid refrigerantand gaseous refrigerant. The receiver 11 is constructed to separate theliquid refrigerant and the gaseous refrigerant from each other and toallow only the liquid refrigerant to be discharged. To this end, theentrance and exit ends of the refrigerant conduit situated inside of thereceiver 11 are extended to the lower portion of the receiver 11.

In order to bypass gaseous refrigerant situated in the receiver 11, avent bypass conduit 12 is provided to connect the receiver 11 to the lowpressure conduit 7 upstream of the accumulator 10. The entrance end ofthe vent bypass conduit 12 is situated in the upper portion of thereceiver 11, so only gaseous refrigerant enters the vent bypass conduit12. A vent valve 13 is provided on the vent bypass conduit 12 andcontrols the flow rate of gaseous refrigerant bypassed. Double dottedarrows indicate the flow direction of the gaseous refrigerant flowingthrough the vent bypass conduit 12.

The portion of the high pressure conduit 6 extended from the receiver 11is constructed to pass through the accumulator 10. This construction isto evaporate the liquid refrigerant of low temperature collected in theaccumulator 10 by using the refrigerant of relatively high temperaturepassing through the high pressure conduit 6. In order to effectivelyevaporate the refrigerant, the portion of the low pressure conduit 7situated in the accumulator 10 is formed in the shape of U, while theportion of the high pressure conduit 6 passing through the accumulator10 is positioned to pass through the interior of the U-shaped portion ofthe low pressure conduit 7.

The outdoor unit 8 further includes a hot gas bypass conduit 14connecting the portion of the high pressure conduit 6 between thecompressor 2 and the condenser 3 to the accumulator 10, and a liquidbypass conduit 15 connecting the downstream side of the receiver 11 andthe upstream side of the accumulator 10. A hot gas valve 16 is situatedon the hot gas bypass conduit 14 to control the flow rate of hot gasbypassed, and a liquid valve 17 is situated on the liquid bypass conduit15 to control the flow rate of liquid refrigerant bypassed. Accordingly,when the hot gas valve 16 is opened, a portion of hot gas dischargedfrom the compressor 2 flows along the hot gas bypass conduit 14 in thedirection indicated by the dotted arrow of FIG. 1; when the liquid valve17 is opened, a portion of liquid refrigerant discharged from thereceiver 11 flows along the liquid bypass conduit 15 in the directionsindicated by the double dotted arrow of FIG. 1.

A plurality of indoor units 9 are arranged in parallel. Each of theindoor units 9 includes an electronic expansion valve 4 and anevaporator 5. Consequently, a plurality of indoor units 9 are connectedto a single outdoor unit 8. The capacities and shapes of indoor unitsmay be identical with or different from one another.

As depicted in FIGS. 2a and 2 b, a variable capacity compressorcontrolled in a pulse width modulation fashion is employed as thecompressor 2. The compressor 2 includes a casing 20 provided with aninlet 18 and an outlet 19, a motor 21 situated in the casing 20, arotating scroll 22 rotated by the rotating force of the motor 21, and astationary scroll 24 defining a compressing chamber 23 together with therotating scroll 22. A bypass conduit 25 is attached to the casing 20 toconnect a position over the stationary scroll 24 to the inlet 18, and aPWM valve (Pulse Width Modulated Valve) 26 in the form of a solenoidvalve is mounted on the bypass conduit 25. In FIG. 2a, the PWM valve 26is OFF and closes the bypass conduit 25. In this state, the compressor 2discharges refrigerant. This state is referred to as “a loading state”,and in this state the compressor 2 is operated at 100% capacity. In FIG.2a, the PWM valve 26 is ON and opens the bypass conduit 25. In thisstate, the compressor 2 does not discharge refrigerant. This state isreferred to as “a unloading state”, and in this state the compressor 2is operated at 0% capacity. Power is supplied to the compressor 2regardless of the loading and unloading states, and the motor 21 isrotated at a constant speed. When power is not supplied to thecompressor 2, the motor 21 is not rotated and the compressor 2 is notoperated.

As shown in FIG. 3, the compressor 2 periodically undergoes the loadingand unloading states during its operation. Loading time and unloadingtime vary according to required cooling capacity. During the loadingtime the temperature of the evaporator 5 is decreased because thecompressor 2 discharges refrigerant, while during the unloading time thetemperature of the evaporator 5 is increased because the compressor 2does not discharge refrigerant. In FIG. 3, the hatched portions indicatethe amount of discharged refrigerant. A signal for controlling loadingand unloading times is referred to as a duty control signal. In theembodiments of the present invention, the capacity of the compressor 2is varied in such a way that the loading and unloading times are variedaccording to the required total cooling capacity of the compressor 2while each period is kept constant, for example, 20 seconds.

FIG. 4 is a block diagram showing the system for controlling thestarting of an air conditioner in accordance with the present invention.As illustrated in FIG. 4, the outdoor unit 8 includes an outdoor controlunit 27 that is connected to the compressor 2 and the PWM valve 26 totransmit and receive a signal. The outdoor control unit 27 is connectedto an outdoor communication circuit unit 28 to transmit and receivedata, and connected to the vent valve 13, the hot gas valve 16 and theliquid valve 17 to control the operation of these valves if necessary.Each of indoor units 9 includes an indoor control unit 29. A temperaturedetecting unit 30 and a temperature setting unit 31 are connected to theinput port of the indoor control unit 29, and the electronic expansionvalve 4 is connected to the output port of the indoor control unit 29.The temperature detecting unit 30 is a temperature sensor for sensingthe temperature of a room to be air-conditioned. Each indoor unit 9includes an indoor communication circuit unit 32 connected to an indoorcontrol unit 29 to transmit and receive data. The outdoor communicationcircuit unit 28 and the indoor communication circuit unit 32 areconstructed to transmit and receive data in a wire or wireless fashion.

In the present invention, the operations of the compressor 2 are dividedinto a normal operation and a starting operation. The normal operationdesignates the operation of the compressor that will be performedaccording to information on a required cooling capacity transmitted fromthe indoor unit after power is applied to the compressor and thestarting of the compressor has been completed, while the startingoperating designates the operation of the compressor that will beperformed to start the compressor when a starting signal is transmittedto the compressor.

In a normal operation mode, the indoor control unit 29 receives signalsfrom the temperature detecting unit 30 and the temperature setting unit31, and calculates the required cooling capacity of the indoor unit 9 onthe basis of the difference between an indoor temperature and a settemperature. Additionally, the indoor control unit 29 has information onthe cooling capacity of the indoor unit itself, and can calculate arequired cooling capacity on the basis of the difference between anindoor temperature and a set temperature and the cooling capacity of theindoor unit itself. The required cooling capacity of each indoor unitcalculated as described above is transmitted through the communicationcircuit units 28 and 32 to the outdoor control unit 27. The outdoorcontrol unit 27 calculates a total required cooling capacity to whichthe required cooling capacities of all the indoor units 9 add up. Thecompressor 2 is operated with its loading time and unloading timealternating with each other, which are preset depending on the totalrequired cooling capacity.

With reference to FIG. 5, a pressure balancing process prior to astarting operation and the starting operation are described. First, theoutdoor control unit 27 determines whether the compressor 2 is stopped(S101). If the compressor 2 is stopped, the electronic expansion valve 4and the vent valve 13 are completely opened (S102 and S103). It isdetermined whether thirty seconds have passed (S103). If thirty secondshave passed, the hot gas valve 16 is opened. Thereafter, it isdetermined whether two minutes and thirty seconds, have passed after thehot gas valve 16 is opened (S105, three minutes after the electronicvalve 4 and the vent valve 13 are opened). If two minutes and thirtyseconds have passed, the electronic expansion valve 4, the vent valve 13and the hot gas valve 16 are closed (S106). The reason why the pressurebalancing process of three minutes is performed is to reduce startingload at the early stage of starting by balancing high and low pressurein a cycle. In such a case, three minutes is a time required to balancehigh and low pressure in the cycle, but the time may be changeddepending on particular systems.

Subsequently, the starting operation will be described. The startingoperation is performed under the control of the outdoor control unit 27.First of all, it is determined whether a starting signal for thecompressor 2 is inputted (S107). If the starting signal is inputted, thecompressor 2 is operated, the electronic expansion valve 4 is closed andthe hot gas valve 16 and the vent valve 13 are opened (S109). In thiscase, the period of a duty control signal for the normal operation. Thereason why the period of the starting operation is set to be shorterthan the period of the normal operation is that is the compressor 2 isoperated by the periods of the normal operation, pressure fluctuationbecomes great, thereby deteriorating the reliability of the compressor 2and causing the safe starting of the compressor 2 to be difficult.Additionally, when the unloading time is relatively long during a normaloperation, the starting of the compressor 2 takes a long time; whilewhen the loading time is relatively long, a pressure drop becomes greatand liquid refrigerant may flow from the accumulator 10 to thecompressor 2. Accordingly, if the loading time is determined as beingrelatively short and a loading operation is frequently performed, thestarting of the compressor can be accomplished rapidly and safely.

In this embodiment, the period of the starting operation is 20 to 80% ofthe period of the normal operation, preferably 50%. The reason why thelowermost limit of the period of the starting operation is determined as20% is that the loading time and the unloading time are set by thesecond and there is a restriction in the reduction of the lowermostlimit. The reason why the uppermost limit is determined as 80% is thatif the uppermost limit is determined as more than 80%, there is nearlyno effect of the reduction of the period. Therefore, when the period ofthe normal operation is twenty seconds, the period of the startingoperation is four to sixteen seconds, preferably, ten seconds.

During the starting operation, the compressor is operated at 20 to 50%modulation. 20% modulation means that the compressor is operated while atwo-second loading time and an eight-second unloading time arealternated, and 50% modulation means that the compressor is operatedwhile a five-second loading time and a five-second unloading time arealternated. However, 30% modulation is preferable. In this case, aloading and unloading time ratio is 3:7. The reasons why the startingoperation is performed at 50% or less modulation are that a limitationis imposed on an increase in modulation because the starting operationis not a normal operation and the reliability of the compressor may bedeteriorated because a great pressure drop occurs due to an increase inmodulation in a low temperature starting operation.

The reason why all the electronic expansion valves 4 are closed whilethe starting operation is performed is to prevent liquid refrigerant,which is contained in the receiver 11 and the evaporator 5 and haspassed through the condenser 3, from entering the accumulator all atonce and, thereafter, the compressor 2. Additionally, the electronicexpansion valves 4 are closed, so the portion of the refrigerant conduitbetween each evaporator 5 and the compressor 2 and the inlet of thecompressor 2 are rapidly depressurized, thereby allowing rapid startingto be accomplished.

In the meantime, when the compressor 2 is operated while all theelectronic expansion valves 4 are closed, the pressure of refrigerantbetween each electronic expansion valve and the compressor 2 greatlydrops and refrigerant is not circulated normally, resulting in theoverheating of the compressor 2. Thus the hot gas valve 16 is opened toconnect the exit side of the compressor 2 with upstream of theaccumulator 10. Accordingly, a portion of hot gas enters the accumulator10, so the pressure of refrigerant situated in the accumulator 10 isprevented from greatly dropping and the compressor 2 is normallyoperated.

In addition, since refrigerant is not circulated normally while all theelectronic expansion valves 4 are closed, refrigerant condensed in thecondenser 3 cannot enter the receiver 11 rapidly. Accordingly, liquidrefrigerant is allowed to flow into the receiver 11 in such a way thatgaseous refrigerant contained in the receiver 11 is discharged to thelow pressure side by opening the vent valve 13.

The liquid valve 17 is opened when the degree of overheating ofrefrigerant sucked into the compressor 2 is high and a liquid ingredientis required to be supplemented.

In the meantime, STEP 108 is performed for about one to five minutes,preferably, one minute. Accordingly, it is determined whether STEP 108has been performed for one minute (S109). If so, the starting operationis stopped; while if not, STEP 108 is continued to be performed. Thetime of starting operation is determined not only to achieve the goal ofstarting operation but also to rapidly start a cooling operation. Whensafe starting is primarily considered, it is desirable to perform thestarting operation for a sufficient time. If so, the normal operation orthe cooling operation is delayed. Although in this embodiment the timeof the starting operation is one minute, five minutes may be selected ifa safe starting operation is pursued though a cooling operation issomewhat delayed.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides a system and methodfor controlling the starting of an air conditioner, in which a pulsewidth modulated compressor is employed and the electronic expansionvalve, the hot gas valve and the vent valve are suitably controlled,thereby allowing the starting of the air conditioner to be performedrapidly and safely. Additionally, the system and method for controllingthe starting of an air conditioner is capable of preventing the inflowof liquid refrigerant in the air conditioner while the compressor isoperated.

What is claimed is:
 1. A system for controlling starting operation of anair conditioner, comprising: a compressor controlled in a pulse widthmodulation manner according to a duty control signal; an electronicexpansion valve for expanding refrigerant compressed in said compressor;a high pressure conduit connecting the exit side of said compressor andthe inlet side of said electronic expansion valve; a low pressureconduit connecting the exit side of said electronic expansion valve andthe inlet side of said compressor; a bypass conduit connected at itsfirst end to said high pressure conduit and at its second end to saidlow pressure conduit; a flow rate regulating valve mounted on saidbypass conduit for regulating a flow rate of fluid flowing through saidbypass conduit; and a control unit for controlling said electronicvalve, said flow rate regulating valve and said compressor during astarting operation of said compressor in such a way that said electronicexpansion valve is closed, said flow rate regulating valve is open andsaid compressor being controlled by a duty control signal having aperiod shorter than a period of a duty control signal for a normaloperation.
 2. The system according to claim 1, further comprising: anaccumulator mounted on said low pressure conduit, wherein said bypassconduit is a hot gas bypass conduit connecting a high pressure conduitbetween said compressor and said condenser and said accumulator, andsaid flow rate regulating valve is a hot gas valve mounted on said hotgas bypass conduit.
 3. The system according to claim 1, furthercomprising an accumulator mounted on said low pressure conduit, and areceiver mounted on a high pressure conduit downstream of saidcondenser, wherein said bypass conduit is a vent bypass conduitconnecting said receiver and a upstream side of said accumulator, andsaid flow rate regulating valve is a vent valve mounted on said ventbypass conduit.
 4. The system according to claim 1, wherein said periodof said duty control signal of said compressor for said startingoperation is 20 to 80% of said period of said duty control signal ofsaid compressor for said normal operation.
 5. The system according toclaim 1, wherein said compressor is operated at a loading and unloadingtime ratio of 2:8 to 5:5 during said starting operation of thecompressor.
 6. The system according to claim 1, said starting operationof the compressor is performed for one to five minutes.
 7. The systemaccording to claim 1, wherein said duty signal has a period of four tosixteen seconds during said starting operation of the compressor.
 8. Asystem for controlling the starting of an air conditioner, comprising: acompressor controlled in a pulse width modulation manner according to aduty control signal; an electronic expansion valve for expandingrefrigerant compressed in said compressor; a high pressure conduitconnecting the exit side of said compressor and the inlet side of saidelectronic expansion valve; a low pressure conduit connecting the exitside of said electronic expansion valve and the inlet side of saidcompressor; a bypass conduit connected at its first end to said highpressure conduit and at its second end to said low pressure conduit; aflow rate regulating valve mounted on said bypass conduit for regulatinga flow rate of fluid flowing through said bypass conduit; and a controlunit for controlling said flow rate regulating valve, said electronicexpansion valve and said compressor to prevent liquid refrigerant fromentering said compressor during a starting operation of said compressor.9. A method for controlling the starting of an air conditioner,comprising: determining whether a starting signal is inputted to acompressor controlled in a pulse width modulation according to a dutycontrol signal; and operating said compressor for a predetermined timewhile closing an electronic expansion valve and opening a flow rateregulating valve mounted on a bypass conduit connecting exit and inletsides of said compressor, when said starting signal is inputted.
 10. Themethod according to claim 9, wherein in said compressor operating isperformed in such a way that said compressor is operated by a dutycontrol signal having a period shorter than a period of a duty controlsignal for a normal operation.
 11. The method according to claim 9,wherein said compressor operating is performed in such a way that saidcompressor is operated by a duty control signal having a periodcorresponding to 20 to 80% of a period of a duty control signal for anormal operation.
 12. The method according to claim 9, wherein saidcompressor operating is performed at a loading and unloading time ratioof 2:8 to 5:5.
 13. The method according to claim 9, wherein saidcompressor operating is performed for one to five minutes.